1. Field of the Invention
This invention relates to methods of manufacturing calibrated temperature responsive switches wherein elongated contact elements are secured by hardening a hardenable material around supporting portions of the elements.
2. Description of the Prior Art
In the manufacture of the prior art switches, such as those described in my U.S. Pat. No. 3,913,054, elongated contact elements are secured by hardening a hardenable material around anchor or supporting portions of the contact elements while the contact ends are held in engagement at the calibration or operating temperature of the thermally responsive switch. Hardenable materials, such as the magnesium oxysulfate base cement supplied in powder form by Sauereisen Cements Company, Pittsburgh, Pennsylvania, USA under the designation Plastic Porcelatin No. 30 which is mixed with water when used, are limited to a particular range of temperatures at which the materials can be hardened or cured; for example mixtures of water and inorganic chemical-setting cements generally cannot be set at temperatures in excess of 100.degree. C. or below 0.degree. C. Thus such prior art thermal switches could only be calibrated at temperatures in the range of the selected hardenable material; for calibration temperatures outside the range of a preferred hardenable material, such as the magnesium oxysulfate and water base mixture, other hardenable materials having higher or lower curing temperatures and which were substantially inferior had to be substituted. For example, thermal setting organic or polymer resins can be selected having setting temperatures substantially above the boiling temperature of water; however such organic materials produce contamination of the contacts from vaporizing, outgassing or decomposition of the organic materials to produce unreliable and defective thermal responsive switches.
U.S. Pat. Nos. 2,745,924, 3,148,258, 3,230,607 and 3,670,281 also disclose processes wherein hardenable materials are cured or hardened to set thermal responsive contact elements at the calibration temperature. The latter U.S. Pat. No. 3,670,281 discloses a gravity biased cylindrical plug having a lower tapered end for engaging the upper ends of contact elements to exert a small force on the contact elements to maintain the contact ends of the elements in engagement during the curing cycle at the desired operating temperature of the switch.